1. Field of the Invention
The present invention relates to a drive force control apparatus and particularly relates to a drive force control apparatus of a riding type vehicle that detects an abnormality of the drive force control apparatus.
2. Description of Related Art
An electronic throttle valve controls an opening degree of a throttle valve by an electronic control to control an intake amount of an engine (internal combustion engine) to realize low emission gas and low fuel cost. Such a construction is already adopted in portions of passenger vehicles.
In adopting an electronic throttle valve for a motorcycle, a drive motor for controlling an opening degree of a throttle valve needs to be arranged compactly while avoiding, interference with a fuel injection valve arranged at an intake path. Therefore, although a compact electronic throttle control apparatus mountable to a motorcycle is proposed in prior art such as JP-A-2002-256895, an electronic throttle control apparatus has not been adopted yet in motorcycles due to their inherent restrictions.
The electronic throttle valve is provided with a function for cutting the drive of the throttle valve by an electronic motor when some abnormality is brought about in a control system to return the throttle valve in a fully closing direction by an urge force of a spring (see, for example, JP-A-2003-201866).
In order to execute this function, a means for detecting that an abnormality is brought about in a control system of the electronic throttle valve is needed. For example, an opening degree of the throttle valve may be detected by a throttle sensor, and a signal of the throttle sensor needs to be constantly monitored in order to detect an abnormal output of the throttle sensor.
When the throttle sensor is otherwise normal, and an instantaneous abnormal signal is caused by noise or the like, although a normal state is recovered immediately, the state is nevertheless determined as an abnormality.
In order to exclude such instantaneous abnormal signal detection, a determination delay time period longer than a signal width of noise or the like may be provided. When an abnormal output continues for the determination delay time period, an abnormality is finally determined.
However, there is a concern that even when a control system becomes truly abnormal, the control of the throttle valve based on the abnormal output is continued until elapse of the determination delay time period. In particular, when applied to a riding type vehicle, a change in vehicle behavior is increased.
In JP-A-10-238389, when an abnormality of a throttle sensor is detected, a control amount of a throttle opening degree is set to a predetermined value (tentative abnormality control), and the throttle control is stopped when the abnormality continues after a determination delay time period has elapsed.
According to this method, a determination delay time before stopping the throttle control after detecting an abnormality is provided, and therefore, an abnormality detection due to an instantaneous abnormal signal by noise or the like is excluded. Further, the control amount of the throttle opening degree can be fixed to a predetermined amount during the determination delay time, and therefore, control of the throttle valve based on the instantaneous abnormal output of the throttle sensor can be avoided.
Although the method described in JP-A-10-238389 promotes reliability of the electronic throttle system, a tentative abnormality control is still carried out during the determination delay time period and therefore, there is a concern of changing vehicle behavior even by noise. Further, when normality is determined and control is returned to a normal state, there is also a concern of changing vehicle behavior.